The present disclosure relates generally to a method for performing geometric dimension and tolerance stack-up analysis and in particular, to a method of performing geometric dimension and tolerance stack-up analysis for an assembly dimension that takes into account both size and geometric tolerances.
Geometric dimension and tolerance (GDT) stack-up analysis is the process of using known dimensions and tolerances of parts to predict the dimension and tolerance of an assembly dimension between mating or adjoining parts. Geometric dimensioning helps to ensure interchangeability of parts and can allow for more variation in tolerances while still producing a functional part. A dimension is a numerical value used to define the size, shape and location of a feature. The term feature is a general term applied to a physical portion of a part (e.g., a surface, a hole, a slot). Feature of size refers to one cylindrical or spherical surface, or a set of two parallel plane surfaces, each being associated with a toleranced size dimension. Assembly dimensions include items such as clearances, gaps and interferences. Clearances refers to the clearance, or the maximum intended difference between mating parts, that exists between the mating parts under all tolerance conditions. Interference refers to the requirement that the mating parts be pressed or forced together under all tolerance conditions. Gaps are the linear distance between two planes or surfaces.
Tolerances can be classified into two groups: size tolerances and geometric tolerances. Size tolerances control the size of a part and create the inherent looseness of an assembly and must be considered in a stack-up analysis. When only a tolerance of size is specified, the limits of size prescribe the extent to which variations in geometric form, as well as size, are allowed. In other words, a feature cannot extend beyond a boundary of perfect form at maximum material condition (MMC). Geometric tolerances along with size tolerances contribute to the tolerance of shape, angularity, profile and location of an assembly. Typically, geometric tolerances are categorized in terms of five types of tolerances including: form, orientation, profile, location and run-out.
One feature or feature of size may have more than one geometric tolerance and a size tolerance. Different geometric tolerances may interact with each other when they apply to the same feature or feature of size. When many features or features of sizes are involved in an assembly, stack-up analysis can get very complicated.
One aspect of the invention is a method for performing geometric dimension and tolerance stack-up analysis for an assembly. The method comprises receiving a target assembly dimension for stack-up analysis, where the assembly includes at least one part. The method further comprises receiving a feature corresponding to the part and receiving feature tolerance data associated with the feature. The feature tolerance data includes at least one of size tolerance and geometric tolerance. Stack-up rules are accessed in response to receiving the feature tolerance data. The stack-up rules include instructions to determine if a form tolerance, an orientation tolerance and a profile tolerance should be included in a stack-up tolerance for the feature. The stack-up rules also include formulas to calculate a nominal dimension and the stack-up tolerance for the feature when the feature tolerance data applies to features of sizes. The nominal dimension and the stack-up tolerance are derived in response to the stack-up rules and the feature tolerance data. Stack-up analysis is performed in response to the nominal dimension and the stack-up tolerance. Performing stack-up analysis results in a mean and standard deviation for the target assembly dimension.
Another aspect of the invention is a system for performing geometric dimension and tolerance stack-up analysis for an assembly. The system comprises a network and a host system in communication with the network. The host system includes software to implement a method. The method comprises receiving a target assembly dimension for stack-up analysis over the network, where the assembly includes at least one part. The method further comprises receiving a feature corresponding to the part over the network and receiving feature tolerance data associated with the feature over the network. The feature tolerance data includes at least one of size tolerance and geometric tolerance. Stack-up rules are accessed in response to receiving the feature tolerance data. The stack-up rules include instructions to determine if a form tolerance, an orientation tolerance and a profile tolerance should be included in a stack-up tolerance for the feature. The stack-up rules also include formulas to calculate a nominal dimension and the stack-up tolerance for the feature when the feature tolerance data applies to features of sizes. The nominal dimension and the stack-up tolerance are derived in response to the stack-up rules and the feature tolerance data. Stack-up analysis is performed in response to the nominal dimension and the stack-up tolerance. Performing stack-up analysis results in a mean and standard deviation for the target assembly dimension.
A further aspect of the invention is a computer program product for performing geometric dimension and tolerance stack-up analysis for an assembly. The computer program product comprises a storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method. The method comprises receiving a target assembly dimension for stack-up analysis, where the assembly includes at least one part. The method further comprises receiving a feature corresponding to the part and receiving feature tolerance data associated with the feature. The feature tolerance data includes at least one of size tolerance and geometric tolerance. Stack-up rules are accessed in response to receiving the feature tolerance data. The stack-up rules include instructions to determine if a form tolerance, an orientation tolerance and a profile tolerance should be included in a stack-up tolerance for the feature. The stack-up rules also include formulas to calculate a nominal dimension and the stack-up tolerance for the feature when the feature tolerance data applies to features of sizes. The nominal dimension and the stack-up tolerance are derived in responsive to the stack-up rules and the feature tolerance data. Stack-up analysis is performed in response to the nominal dimension and the stack-up tolerance. Performing stack-up analysis results in a mean and standard deviation for the target assembly dimension.
Further aspects of the invention are disclosed herein. The above discussed and other features and advantages of the invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings.